linux-kernel - Re: [PATCH] of: introduce event tracepoints for dynamic device

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Message-ID: <87vapyttds.fsf@concordia.ellerman.id.au>
Date:   Fri, 21 Apr 2017 11:57:19 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Frank Rowand <frowand.list@...il.com>,
        Tyrel Datwyler <turtle.in.the.kernel@...il.com>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>, robh+dt@...nel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, nfont@...ux.vnet.ibm.com,
        rostedt@...dmis.org, mingo@...hat.com
Subject: Re: [PATCH] of: introduce event tracepoints for dynamic device_node lifecyle

Frank Rowand <frowand.list@...il.com> writes:

> On 04/20/17 09:51, Tyrel Datwyler wrote:
>> On 04/19/2017 09:43 PM, Frank Rowand wrote:
...
>>> Which ends up being this code:
>>>
>>>    of_platform_default_populate_init()
>>>       of_platform_default_populate()
>>>          of_platform_populate()
>>>             [[ of_find_node_by_path("/") ]]
>>>                [[ of_find_node_opts_by_path(path, NULL) ]]
>>>                   of_node_get(of_root)
>>>
>>> Note that some functions can be left out of the ARM call stack, with
>>> a return going back more than one level.  The functions in the call
>>> list above that are enclosed in '[[' and ']]' were found by source
>>> inspection in those cases.
>> 
>> The same thing is encountered in ppc64 stack traces. I assume it is
>> generally inlining of small functions, but I've never actually verified
>> that theory. Probably should take the time to investigate, or just ask
>> someone.
>
> Yes, inlining small functions is one reason for this.
>
> Another case I often find is that when function A calls function B calls
> function C.  If the final statement of function B is 'return C()' then
> there is no need for function C to return through function B, it can
> instead return directly to function A.

It's called "Tail call optimisation", and that's more or less a good
description.

cheers